Process for preparing improved lithographic printing plates by brushgraining with alumina/quartz slurry

Abstract

Provided herein is a brushgraining process to improve the quality of lithographic printing plate substrate surfaces. In the process, the surface is brushed in an aqueous slurry comprising a mixture of particulates of alumina and quartz in a weight ratio range 95:5 to 5:95, with the particulates being in the size range of 1-20 microns. Such a process surprisingly lessens the number of scratches produced on the substrate surface than when compared to using alumina alone or quartz alone or a mixture of alumina and quartz with particle sizes higher than the range disclosed.

What is claimed is: 
     
       1. A process to prepare a lithographic printing plate, sequentially comprising: (a) providing a substrate made of a suitable metal;   (b) brushgraining said substrate in an aqueous slurry comprising a mixture of particulates, wherein said mixture comprises alumina and quartz in a weight ratio in the range of 95:5 to 5:95, and wherein said particulates have particle size in the range 1-20 microns;   (c) conditioning said surface polyvinylphosphonic acid maintained at a pH range of about 2.5 to 6;   (d) applying a photosensitive layer;   (e) imagewise exposing said photosensitive layer to suitable actinic radiation; and   (f) developing said exposed layer in a suitable developer thereby resulting in an image commensurate with the type of said photosensitive layer in step (d) above.   
     
     
       2. The process as described in claim 1, wherein said substrate is made of aluminum or steel. 
     
     
       3. The process as described in claim 1, wherein said mixture comprises alumina and quartz in a weight ratio in the range of 90:10 to 80:20. 
     
     
       4. The process as described in claim 1, wherein said particle size is in the range 1-10 microns. 
     
     
       5. The process as described in claim 1, wherein said particle size is in the range 3-6 microns. 
     
     
       6. The process as described in claim 1, wherein said graining is done using a single brush. 
     
     
       7. The process as described in claim 1, wherein said graining is done using a plurality of brushes. 
     
     
       8. The process as described in claim 1, wherein said aqueous slurry has a solids concentration of about 5-50 weight percent. 
     
     
       9. The process as described in claim 1, wherein said aqueous slurry has a solids concentration of about 15-30 weight percent. 
     
     
       10. The process as described in claim 1, wherein said photosensitive layer comprises a photosensitive compound of positive type. 
     
     
       11. The process as described in claim 10, wherein said positive photosensitive compound is a sulfonic acid ester of an orthoquinone diazide. 
     
     
       12. The process as described in claim 1 wherein said photosensitive layer comprises a photosensitive compound of negative type. 
     
     
       13. The process as described in claim 12, wherein said negative photosensitive compound is a diazonium compound. 
     
     
       14. The process as described in claim 13, wherein said diazonium compound is a polycondensation product of 3-methoxy-4-diazo diphenyl amine sulfate and 4,4'-bismethoxy methyl-diphenyl ether, precipitated as mesitylene sulfonate. 
     
     
       15. The process as described in claim 1, wherein said actinic radiation has a wavelength range 300-400 nm. 
     
     
       16. The process as described in claim 1, wherein said developer is an aqueous developer selected from the group consisting of sodium octyl monosulfate, potassium decyl monosulfate, lithium dodecyl monosulfate and combinations thereof. 
     
     
       17. The process as described in claim 1, wherein said brushgrained substrate is further oxidized. 
     
     
       18. A lithographic printing plate prepared by the process described in claim 1. 
     
     
       19. A process to prepare a lithographic printing plate, sequentially comprising: (a) providing an aluminum substrate;   (b) brushgraining said aluminum substrate in an aqueous slurry comprising a mixture of particulates, wherein said mixture comprises alumina and quartz in a weight ratio in the range of 95:5 to 5:95, and wherein said particulates have particle size in the range 1-20 microns;   (c) conditioning said surface with polyvinylphosphonic acid maintained at a pH range of about 2.5 to 6.   (d) applying a photosensitive layer;   (e) imagewise exposing said photosensitive layer to suitable actinic radiation; and   (f) developing said exposed layer in a suitable developer thereby resulting in an image commensurate with the type of said photosensitive layer in step (d) above.   
     
     
       20. The process as described in claim 19, wherein said mixture comprises alumina and quartz in a weight ratio in the range of 90:10 to 80:20, and wherein said particle size is in the range 1-10 microns. 
     
     
       21. The process as described in claim 19, wherein said brushgrained aluminum substrate is further oxidized. 
     
     
       22. A process for graining lithographic substrate surfaces, wherein said graining is done in an aqueous slurry comprising a mixture of particulates, wherein said mixture comprises alumina and quartz in a weight ratio in the range of 95:5 to 5:95, and wherein said particulates have particle size in the range 1-20 microns. 
     
     
       23. The process as described in claim 22, wherein said substrate is made of aluminum.